selftests/landlock: Add tests for quiet flag with net rules

selftests/landlock: Add tests for quiet flag with net rules

Tests that:
- Quiet flag works on network rules
- Quiet flag applied to unrelated ports has no effect
- Denied access not in quiet_access_net is still logged

This is not as thorough as the fs tests, but given the shared logic it
should be sufficient.  There is also no "optional" access for network
rules.

Signed-off-by: Tingmao Wang <m@maowtm.org>
Assisted-by: GitHub-Copilot:claude-opus-4.7 copilot-review
Link: https://patch.msgid.link/364fbd08081318d64bc23049d3a7721f0a3a3624.1781228815.git.m@maowtm.org
Signed-off-by: Mickaël Salaün <mic@digikod.net>